114 
Fishery Bulletin 11 7(1-2) 
Table 4 
Estimates, with 95% confidence intervals (95% CIs), of 
the parameters for the von Bertalanffy growth model 
used to examine differences in growth parameters be¬ 
tween sexes for blue sharks (Prionace glauca) in the 
western North Pacific Ocean. The parameters are the 
theoretical asymptotic length (L„), measured in centi¬ 
meters in precaudal length; the annual growth coeffi¬ 
cient ( k ); and the theoretical age, measured in years, at 
zero length ( t 0 ). 
Sex 
Parameter 
k 
to 
Male 
Estimate 
284.9 
0.117 
-1.35 
Lower 95% Cl 
258.0 
0.109 
-1.44 
Upper 95% Cl 
294.6 
0.145 
-0.90 
Female 
Estimate 
257.2 
0.146 
-0.97 
Lower 95% Cl 
246.6 
0.131 
-1.17 
Upper 95% Cl 
267.6 
0.163 
-0.79 
dition was 6.7 years (95% Cl: 6.3-7.2 years) (Fig. 60, 
an age that is 1.4 years older than the estimate of age 
at 50% maturity for females. 
Discussion 
In this study, we simultaneously used a burn method 
(Fujinami et al., 2018a) for specimens less than 200 cm 
PCL and a thin-sectioning method (e.g., Matta et al., 
2017) for individuals greater than 200 cm PCL. Ages 
of blue sharks of the North Pacific Ocean have been 
determined previously by using silver nitrate impreg¬ 
nation and thin-sectioning methods (Table 5). The con¬ 
vex and concave structures that we observed by using 
the burn method correspond with the translucent and 
opaque bands apparent in silver nitrate impregnation 
(Fujinami et al., 2018a) and sectioning with alizarin 
red for older specimens, respectively, indicating that 
our approach with simultaneous use of a burn method 
and sectioning provides comparable age estimates for 
the size range compared. The precision of ages esti¬ 
mated by using a burn method and silver nitrate im¬ 
pregnation was high for small- and medium-sized in¬ 
dividuals (<200 cm PCL), particularly when the burn 
method was used, and the precision for both methods 
was lower for older specimens (Fujinami et al., 2018a). 
Use of the burn method tended to result in counts of 
fewer bands than the use of the thin-sectioning method 
when band counts exceeded 11, for a subsample (n= 97) 
of individuals exceeding 190 cm PCL (Suppl. Table 2) 
(online only). Shark vertebral growth and band-pair de¬ 
position are both tightly linked to somatic growth; 
therefore, vertebral growth decreases in older speci¬ 
mens (i.e., the vertebral edge narrows in older sharks) 
(Natanson et al., 2018). Such limited growth for older 
specimens is detectable in thin sections; however, it is 
much more difficult to determine in intact vertebrae 
(Matta et al., 2017). Consequently, we believe that the 
simultaneous use of burn and thin-sectioning methods 
provides a more accurate estimate of age than the use 
of only a single method. 
We observed banding patterns in blue sharks simi¬ 
lar to those reported previously. Nakano (1994) sug¬ 
gested that the birth band of blue sharks of the North 
Pacific Ocean forms just after summer and that subse¬ 
quent growth bands form annually in the boreal win¬ 
ter (on the basis of silver nitrate impregnation). Slow 
growth-zone formation from late autumn to winter and 
fast growth-zone formation during spring and summer 
also were reported by Wells et al. (2017) on the basis 
of research that involved analysis of vertebrae from 
blue sharks injected with oxytetracycline and tagged 
and recaptured in the eastern North Pacific Ocean. 
Our results, from the use of both burn and thin-sec¬ 
tioning methods, are similar to those of previous stud¬ 
ies in the North Pacific Ocean: narrow bands (slow 
growth) are formed in the winter, and broad bands 
(fast growth) are formed in the summer. Therefore, 
we assert that growth-band deposition after the birth 
band in blue sharks of the North Pacific Ocean occurs 
annually, regardless of the aging technique and geo¬ 
graphic area of sampling used to estimate ages. Con¬ 
sequently, the increment between the first and second 
bands represents about 6 months of growth (tentative 
birth period in June, subsequent band formation in 
December)—a result similar to that reported by Na¬ 
kano (1994). Similar patterns also have been reported 
in other species, such as the blacktip shark ( Carcha - 
rhinus lijnbatus ) (Branstetter, 1987) and the shortfin 
mako (Isurus oxyrinchus) (Semba et al., 2009). Several 
triggers, such as environment experienced (e.g., wa¬ 
ter temperature), prey availability, physiological dif¬ 
ferences, and movement patterns, might be related to 
postnatal band formation (e.g., Natanson and Cailliet, 
1990; Wells et al., 2017). 
The asymptotic length of blue sharks in the east¬ 
ern North Pacific Ocean (Cailliet and Bedford, 1983; 
Blanco-Parra et al., 2008) is much smaller than that of 
blue sharks in the western North Pacific Ocean (Tana¬ 
ka et al., 1990; Nakano, 1994; and herein, see Table 
5). To provide quantitative estimation for growth pa¬ 
rameters, access to specimens from neonate to larger 
and older individuals is necessary because estimates 
of growth parameters generally are affected by small 
sample sizes of small or large specimens (Campana, 
2001; Goldman et al., 2012). Growth parameters we 
report for this study differ from those reported for 
sharks in the eastern North Pacific Ocean (Cailliet 
and Bedford, 1983; Blanco-Parra et al., 2008), possibly 
because few larger and older specimens (most individu¬ 
als were less than 200 cm PCL) were represented in 
samples in those studies. The size range of specimens 
reported from the central South Pacific Ocean by Joung 
et al. (2017) is similar to the range we report, as are 
estimates of growth parameters, especially asymptotic 
length (Table 5). However, our estimated female as- 
